Pictures of green flashes

Introduction

Green flashes come in two
common forms,
succinctly described by James Prescott Joule in a
letter to the
Manchester Literary and Philosophical Society in 1869.
First, he noted that “at the moment of
the departure of the sun below the horizon, the last glimpse is coloured
bluish green.” This “last glimpse” flash is associated with the
inferior mirage,
familiar on asphalt roads on sunny days. It is best seen
from a few meters above sea level, and becomes compressed to a thin line
at the horizon when seen from considerable heights.

Joule also observed that “Just at the upper edge, where bands of the sun's
disk are separated one after the other by refraction, each band becomes
coloured blue just before it vanishes.” This second form of flash is
associated with a mock mirage,
which is caused by a
thermal inversion
below eye level; so it is mainly seen from elevated positions.

There are also several less-common forms, but no photographs of them are
available.
I have made animated simulations
of the common forms.

There is also a
page
showing the range of observed colors of flashes, if you just want a quick
look at some good examples.

Links to Pictures on the Web

There are a lot of links to other peoples' sites here; if you find a
broken link, please
tell me about it.

The pictures shown here were all taken with long-focus lenses, and
show considerably more detail than is visible to the naked eye.
Many of the nice flashes here would in fact pass unnoticed without some
optical assistance; see the page on how to
observe
green flashes.

Please respect the copyrights of the original photographers.

I'll start off with a pointer to Les Cowley's atmospheric-optics
website,
which has a fine
section
on green flashes. He's found a good selection of pictures to illustrate
the common types.

Another fine set of blue and violet rims photographed from a
mountain observatory, provided by Christophe Gervier. These
full-resolution images are needed to see all the beautiful
details; but if you find them too large and slow-loading, there's
also a
reduced set
available.

Patrick Muller's extensive sequence shows the progression of the
sunrise very well, including the sequence of colors in this
mock-mirage flash. (Note that some colors in the later,
overexposed images are artifacts.) The first, pre-sunrise
image showing aerosol scattering in the valleys below, and the
final triangular shadow of the mountain are a
nice bonus. (Thanks to Luc Dettwiller for providing the URL!)

There's also a nice GIF animation of a mock-mirage flash at sunset
on his Web pages
here.
The individual frames can be
examined
as well.

Finally, there's a superb sequence of pictures showing
12 mock-mirage flashes at a single sunset, thanks to strong gravity
waves on the numerous inversions. These show both the geometrical
effects of such waves, but the progressive increase in extinction
at short wavelengths as the Sun sank: the first flashes are bright
blue, but become fainter and greener with increasing zenith
distance. Again, click on each image to see it at full resolution!
(Thanks to Luc Dettwiller for bringing this sequence to my attention!)

Guillaume Blanchard's photographs are arranged as a slideshow.
Both mock-mirage and inferior-mirage flashes appear here.
Images 4-7 show the progression of a fine blue flash; image 7
clearly shows the true (red) color of the low Sun in the scattered
light along the distant ridge, demonstrating that the white color
of the overexposed disk in image 4 is an
artifact.
(Thanks to Luc Dettwiller for providing the URL!)

Page back to the “panorama” that precedes it, to see
how the flash developed. Note the strong extinction gradient,
which helpfully dimmed the (normally much brighter) lower image.

Photographed from the top of Bantiger mountain
(950m above SL) near Berne, Switzerland, above a
sea of clouds at around 800m, by Alfred Weiersmüller.
The same site has some other pictures of interest, taken by other
photographers, such as a nice
series
showing the formation of an inferior-mirage flash.

One must be careful here; many of the photographers don't
understand what they have taken, so many of the images are
mislabelled. Some just show
artifacts,
not natural phenomena.

A San Francisco sunset sequence, photographed by
Mila
Zinkova, who has a fine collection of GF photos.
This sunset has mock-mirage flashes, due to a series of inversion
layers. The green color in the upper right-hand image almost
approximates the vividness of the color one sees with the eye.

This sunset shows two inversions: a surface-based inversion that
produces the line just at the sea horizon, and a higher one that
made the mock-mirage flash. George Howard was the photographer.
[The original page has vanished from the Web, but is preserved on the
Wayback Machine at
http://web.archive.org/web/20131028235240/http://www.pbase.com/warthog2100/image/52487119
;
it's also shown on the
SpaceWeather
website.] Notice how the sky darkens rapidly near the sea
horizon, just where the yellow line appears; both are due
to the rapid increase in refraction just above the sea surface.

This page of pictures has links to two shots of the same sunset
flash (the two numbered 7781 and 7782, at the bottom of the page).
With the ship on the horizon, it's like the frontispiece of
O'Connell's book.

Notice that the inferior mirage also produces an inverted image of
the distant clouds. The compression of the inverted images is
quite obvious here.

A very picturesque flash framed by the Golden Gate Bridge,
seen from the Berkeley Marina; taken by Paul Kamen. He has a
video
of this flash, as well! (Compare his video to my
simulation
of such a flash; his proceeds a bit more slowly, because of his
latitude.) Yet another flash with a vessel nearby.

One of Mila Zinkova's recent GF pictures. She has been collecting
flashes since late 2005 in San Francisco. This one turns
out to be a little more complicated than a simple inferior-mirage
flash (I've seen her other frames of this sunset).

Notice the gradation in color within the flash: yellowish in the
center, bluish at the extreme ends. This picture also shows the
effect of atmospheric reddening well in the prominent contrail.
The orangish hue of the sky, and the visibility of blue in the
flash, are indications of extremely clear air.

In addition, there's a small cloud beyond the horizon, miraged by
the same layers near the sea surface that stretch the normally
invisible
green rim
into a green flash. It's to the left of the flash, and about the
same size; notice that it's exactly the same height above
the horizon as the flash.

Mila has links to several more of her pictures of green flashes,
sunset mirages, halos, rainbows, glories, and other atmospheric-optics
phenomena
here.

Jon Adamson's inferior-mirage flash sequence, taken at 5
frames/second with a Canon EOS 20D digital SLR with a 300 MM
Image Stabilized lens, from a ship. The flash is apparent in the
last few frames (on the second page of thumbnails), but you have
to go to the larger images to see it. Part of the sequence is
repeated at higher magnification on the 3rd page of thumbnails
(and their corresponding full-sized images).

A naked-eye flash taken March 30, 1998, from near Scripps
Pier, about 11 meters above sea level.
A
larger high-resolution scan of the same flash is also available.
Note the yellow flash disappearing in the middle of the green one.

I also use this flash as an example on my
Omega page,
where the flash is compared with the image of the whole Sun when
its lower limb was miraged (instead of the upper limb, as in this
picture).

Several pictures taken by Steve Rossi with a fairly short focal
length give a good approximation to the visual appearance of
these phenomena. There is a cloud-top flash as well as several
inferior-mirage flashes.

David Dilworth's excellent example of a cloud-top flash seen
from near sea level. As the dip of the horizon is small here, you
can see that these flashes occur well above the astronomical
horizon. (See the
green-rim page
for details.)

John Coveney caught this mock-mirage flash while on holiday in
Sardinia. The green tips on the lower (yellow) part of the solar
image suggest there may have been an inferior mirage as well.
(Click on the "View on black" link just beneath the image
for an enlarged and much better view of it.)

The red sunset sky — which is the same color as the Sun
at the horizon — is well captured, showing that the
yellow color of the (overexposed) lower image is an
artifact.

Martin Rietze photographed these green and blue flashes in Hawaii.
Be sure to click on the small photos to see the details; the last
picture (in which the vanishing blue flash is hardly seen in the
small version) shows the very last, almost violet stage of his
blue flash. The clouds to its left show the same vertical
stretching as the sliver of the Sun's upper limb — both due
to the inferior mirage, which is the usual cause of flashes seen
in Hawaii.

A fine set of good examples taken by Robert Wagner
from Roque de los Muchachos on La Palma in the Canary Islands.
The blue and violet colors here are helped by the great height
above sea level (2200 meters), which means less atmospheric
reddening when the flashes occur above the clouds instead of the
sea horizon.

The photographer has called my attention to
another
interesting photograph, which shows the “silver
lining” of a cloud with green and blue bits along its upper
edge, and a red lower rim — as well as a nice cloud-top blue
flash from the Sun! The upper “green rim” of a cloud
is ordinarily too attenuated by atmospheric reddening to be
observable; but the photographer is high enough here to be above
much of the atmospheric reddening, making this rare view of
dispersion effects on cloud rims visible.

One of Pekka Parviainen's fine green flashes is down at the end of
this long page of mirage images. He also has a video of the GF sunset.
There's also the bonus of a selection of typical distorted sunsets,
showing many beautiful types of sunset mirages.

Still more of Pekka's mirage and distorted-sunset pictures, with several
green flashes, are available on
his own pages.
Click on the "Sun" item in the menu at the left side of his main page
to find the green-flash pictures.

Paolo Candy has combined a beautiful inferior-mirage flash here
with a solar eclipse, photographed from Madagascar. He has
put his experience with green flashes to work, capturing just
the moment when the film registers green over the whole flash.
There's also a good description of what's going on (in Italian).

This disappeared for several months after he died. It was
temporarily resurrected, but now seems to exist only on the
Wayback Machine. There is an interesting perturbation
of the flash (visible really only in the enlargement at the bottom
of the page) caused by the wake of an airplane.

These interesting pictures were taken at the South Pole sunset of
the year 2000. They show a type of flash produced by strong thermal
inversions. Notice that the blue parts are generally much fainter than
the green ones, and lie outside them. For context, see the accompanying
Sunset
pictures.

A more recent example (polar sunset, 2005), taken by Guillaume
Dargaud. He uses the term “green ray” because that's the
literal translation into English of the term used in his native
French. There's also a nice example of a distorted
moonrise, with green upper rim and red features on the lower one.
Ignore the remarks about the Sun being reflected by a mirage
on the ground; it's seen through a leaky duct, whose upper surface
he confuses with the true horizon. The best pictures show complex
features due to waves on the inversion overhead. Unfortunately,
they were taken with a digital camera and are probably affected by
artifacts.
(Thanks to Andy Beeler for pointing out this site.)

Laurent Laveder's
nice examples of the green and red rims on the rising full Moon,
with a small mock-mirage flash due to waves on a lifted inversion
— an example of
Fraser's
mechanism. Click on the images to
see larger versions, and don't miss the
second page
of images.

In fact, he has yet another
page
of images, showing a fine
time-series
of an
Omega
sunset and the
gradual disappearance
of the upper blue rim, as shown in a series of pictures that
ends
in an inferior-mirage flash.
(Again, click on the pictures to display larger versions.)

A mock-mirage red flash. The green rim is visible at the upper
limb; this, together with the small extinction gradient across the
disk, and the asymmetries of the red flash (indicating waves on a
inversion) suggests that the inversion was above the observer
(which would make this an example of Alistair Fraser's type of
flash).
(Thanks to Luc Dettwiller for pointing out this page.)

This picture was taken at Shonaihama, Yamagata prefecture, by
photographer Hiroyuki Murata, who takes sunset photos there more than
300 days a year.
He says the atmosphere at Shonaihama is unstable and mirages are
often produced.
(Thanks again to Takayuki Kono for pointing out this page,
and for translating the text.)

Oscar Medina's very nice inferior-mirage flash. Notice the
very obvious gap between the flash and the apparent horizon.
(Pacific Beach is the part of San Diego coastline that's nearest
to me; it's just south of La Jolla.) His original inferior-mirage
flash is now accompanied by several more recent flashes, including
some mock-mirage flashes.

His pictures also show some interesting variations in the
dip
of the sea horizon, which I discuss
elsewhere.

A couple of nice inferior-mirage flashes about halfway down the
page, with other sunset pictures. Follow the links by clicking
on the pictures for the May 18 and Sept. 7 sunsets to see the
full sequence; the latter nicely shows the progress of an
Omega due to the inferior mirage.

A fine example of a “cloud-top” flash.
The extreme flattening of this flash shows that it is caused by a
thermal inversion; the fine diagonal structure within the flash
is due to waves on that inversion.

This sequence of 10 images shows the development of a flash
associated with strong thermal inversions. The red band below
the bright yellow image is a mock mirage of the Sun's lower limb;
the discontinuity of colors at the level where the upper image
tails off to sharp points at the sides marks the top of a duct. I have
simulations
of the phenomena produced by ducts; compare this picture with the
third image in the views of a deeper duct seen from
65 m.

Explanation in German and pictures taken by Peter Pammer,
on the Web pages of the
Arbeitskreis Meteore
of the
Verein der Sternfreunde.
Follow the “Bildarchiv”
link at the bottom of the page to see a couple of
mock-mirage flashes, and a fine mock-mirage lunar red flash.

You don't often see such finely recorded visual observations as
these; the GF drawings are down near the end of this page. Don is a
professional artist who specializes in astronomical subjects; his pages
also contain some unusual halo phenomena.

This is a gif animation of a sunset sequence. The mock mirage
shows up very nicely in the 3rd frame of the series, and there is the
corresponding green flash in the 9th frame.
The animation gives a good feel for the progression of forms in this
typical mock-mirage sunset. Associated pages show several
fine rainbows and a beautiful example of anticrepuscular rays.

A couple of sunsets with strong ducting features are shown
down near the end of this page, one with a small green flash in
the upper part. This is one of the
less-common forms that are not
yet well understood.

At the end of Journal entry #20 on this page, you'll find an
Antarctic
flash
very similar in form to the one mentioned just
above, photographed from Mauna Kea. Evidently these
geographically distant flashes — one from the tropics, one
from the polar regions — have a common origin: a strong
thermal inversion.

What's more notable in this wide-angle image is the brightness
gradient in the sky, which illustrates the extinction gradient.
(When the Sun is high, the horizon is brighter than the sky
above it — the opposite of what you see here.)

Not a green flash; but such nice examples of the strong refraction
associated with thermal inversions that a link here seems appropriate.
Caution: some of the pictures show artifacts due to an overexposed solar
image.

Now that you've seen some modern pictures, you might be interested in the
history of green-flash photography. I have a short
page
describing a few “firsts” in this field.

Simulations of green flashes

You might also like to look at some animated
simulations I have prepared to
illustrate the effects of different kinds of atmospheric structures.
Some of these reproduce the general features of certain common types of
green flash remarkably well.

Green flashes on video

Hits …

Occasionally, I'm asked if I have a video of a green flash. No, I don't.
The first person to have posted a good video recording of a GF sunset is
the remarkable Finnish photographer
Pekka Parviainen, who has provided a
downloadable version (as a *.ram file) on the Virtual Finland Web pages.
Pekka seems to be allergic to e-mail, but his address and phone number are
provided on that Web page. He is quite capable in English, so don't
worry that you might need to speak Finnish to communicate with him.

There is a second video of a GF sunset at
The Short Fat Guy On Vacation
but unfortunately for me, this, too, is a RealVideo file, which I can't display.
I have looked at it on the machines in our library; the flash appears to
be an ordinary inferior-mirage flash, and the color (as displayed on the
Macs in the library) is rather pale and unsaturated. The whole sequence
is overexposed, which may partly account for the lack of vivid color in
the flash. This clip seems impressive to people who are not familiar
with green flashes. Pekka's sequences (see previous paragraph) are
better.

Paul Kamen has now made a
7-second
*.avi clip
available, nicely showing an inferior-mirage flash as it unfolds.
A link
to the video is also hosted by Les Cowley.

… and Misses

Another supposed GF video is available at
Crazy Joe's SurfLounge in Hawaii.
The sunset clips are on
this page.
Unfortunately, the nice sunsets show not a trace of a green flash, though
there are indeed a few greenish
digital and
video artifacts
on display — as well as a link to putative green flashes on YouTube,
which is much worse.

Though YouTube contains a couple of rather feeble green flashes, most of
the clips there show nothing resembling a green flash. There are a
few obvious fakes; several video-camera quirks due to the interaction of
wobbly hand-held cameras with autoexposure algorithms (e.g., when the
dark sea fills most of the frame, the camera brightens up the picture,
making ignorant photographers mistakenly think some kind of
“flash” has occurred); a number of common overexposure
artifacts of digital cameras; several sunsets in which the sky is so
cloudy, or so murky with reddening haze, that a green flash could not have
been seen; and many sunsets taken with such a
short focal-length lens that no flash could have been captured, even if
one was present. An amazing number of the clips claiming to show green
flashes just show ordinary sunsets, with nothing visible to suggest why
the photographer made such a claim.

Don't waste your time looking for needles in this haystack of pathetic junk.
The only authentic green flashes I've found there are a couple of very typical
inferior-mirage flashes photographed by Andrew Penketh in 2007 and 2008 at
St. Lucia.
YouTube also has several copies of Paul Kamen's good GF clip, mentioned
above.

Green flashes in movies

There are a few movies that purport to have a green flash, but most show
only clumsy fakes done with crude special effects. However, the 1986
Eric Rohmer film “Le Rayon Vert” (available with English
subtitles as “Summer”) actually has a textbook example of
an inferior-mirage flash, photographed by Philippe Demard. This film is
also available on videotape. The film has many references to the Jules
Verne novel, and a clear exposition of the textbook explanation. Not bad!

Green things that aren't green flashes

Crepuscular rays

By the way, one thing often confused with green flashes is green
crepuscular rays,
as in the picture shown here (thanks to Sabine Mercier, who photographed
this splendid example in Madagascar.)
Another nice
picture
of some green crepuscular rays is on
Chuck Doswell's Web pages.
Perhaps a dozen of the 1000-odd references I've found on
green flashes are reports of crepuscular rays instead.

Crepuscular rays are shadows of objects (usually cumulus clouds, but
sometimes a mountain). If the object is beyond your horizon, you won't see
the obstacle that casts the shadow, just its shadow in the hazy air
above you. (In the picture above,
notice that the ray is darker than the adjacent sky at the same
altitude above the horizon.)
If there are lots of clouds, there may be only a few gaps between them;
then you see bright “rays” between the darker, bluish shadows.

Crepuscular rays typically have time scales of tens of minutes,
as opposed to a few seconds for green flashes. Also, crepuscular rays
have angular lengths of tens of degrees, while an ordinary green flash is
always smaller than the size of the Sun (half a degree), and
usually only just above the resolution threshold of the eye — a few
minutes of arc.

While there is a
“green ray”
rarely associated with green flashes, even
these are usually only a few degrees long, and share the brief time
scale (a few seconds) of the commoner flashes. And as these
green rays
are brighter than their surroundings (unlike the crepuscular rays,
which are darker), even these rare green-ray
displays should not be confused with the much more common crepuscular rays
— most of which are blue rather than green.

There are some spectacular examples of crepuscular rays on the Web, as
well as many more insipid pictures; here
are a few of the better ones:

Greg Smith
has photographed
another striking crepuscular ray;
and as he has no website, has granted permission for me to post it here.
He says, “The photo was taken just after sunset on July 20, 2000,
on the Waikaloa coast of Hawaii (just north of Kona).”
You can see, in the upper part of his picture, some clouds that are probably
similar to the one just over the horizon that is casting a deep blue
shadow on the hazy air. Outside this cloud shadow, the haze is illuminated
by the orange light of the setting Sun. At the lower left in his
picture, just above the horizon, another ray is faintly visible; the two
rays converge to the point just below the horizon where the Sun is.

Crepuscular rays are the shadows of
clouds or distant mountains, often just over the horizon, cast on the hazy
lower atmosphere. Their apparent divergence from the Sun's position is
merely an effect of perspective, as these shadows are all nearly parallel
lines in the air.

Philip W. McKee has sent me
another fine example
that clearly shows the shadows of clouds.
He says,
“I live 22 miles south of Cape Canaveral and our condo is on the first
dune. I try to catch sunrise often. The attached pix were taken off
our balcony in early July, 2001.”
He adds that the picture was taken more than 10 minutes before nominal
sunrise; so these rays, too, are literally “crepuscular” — that is,
twilight.

Ten minutes corresponds to a solar depression of about 2.5° at low
latitudes. The dip of the horizon is 2.5° at a height of a little
over 7 km, so the parts of the cumulus tower higher than that are in full
sunlight. You can see from the shape of the tower that it has flattened
out near the tropopause (probably about 14 km) — notice the weakly
developed “anvil” at the right side. The haze layer is higher than
that; it might be just about at the tropopause. The lower atmosphere is
still in the Earth's shadow, but the high clouds are in sunlight.
If you extrapolate the rays until they converge at the Sun, you find it's
just off the left edge of the picture, and just a little below the
horizon.
Here, a haze layer just above the clouds is illuminated by the
same reddened light of the low Sun as the cumulus towers, whose shadows
on the haze appear blue.
You can see that the “blue rays” here are just the blue sky,
uncontaminated by the reddish haze, which contrasts nicely with them.

Recently, the remarkable photographer and dye-transfer printmaker
Ctein
has put up
an interesting picture
that nicely illustrates how confusion can arise. It shows some
(relatively weak) crepuscular rays, as well as a piece of sky near the Sun
that appears quite greenish at first glance — though if you mask it off,
you can see it's really a greenish yellow, and the perceived green is
mostly due to simultaneous contrast with the purple arc above it.
There is a lot of interesting optics in this picture: the purple arc, the
distortions of the reflected sky by the ripples in the water, clouds that
appear brighter or darker than the surrounding sky depending on location, the
crepuscular rays, and the appearance of green in the sky — so it's worth
waiting for the large (161 kB) image to download.
And it's a beautiful picture, to boot. Go take a look!

Green Sun

Other things occasionally mistaken for green flashes are the
“green Sun”
(a variant of the “blue Moon” phenomenon, which is due to unusual
aerosol scattering), and green aurorae. Both these phenomena last much
longer than green flashes, which are usually visible only a second or
two — the longest flashes on record are about 15 seconds.
The “green Sun”
is usually seen an hour or so before sunset or after sunrise, but
has occasionally been seen even at mid-day; it's usually accompanied by
so much aerosol
extinction
that the Sun becomes invisible before reaching the horizon.
The colors of these non-GF displays are much less saturated than those of
real green flashes; so there should be no confusion.

following the eruption of Krakatoa, which produced a strong
stratospheric haze of nearly constant particle size the previous year.
(Contemporary accounts refer to this aerosol layer as “ash” or
“dust”, but it was almost certainly made up of photochemically
generated droplets of sulfuric acid, resulting from the great quantities
of sulfur dioxide injected into the stratosphere by the eruption.)
The “green Sun” phenomenon was widely observed, and accounts
appeared in all the major scientific journals of the day, as well as
popular versions in newspapers; but I think Michie Smith's paper is one
of the best first-hand accounts.
(He was also an experienced green-flash observer, by the way.)
Unfortunately, he concluded that the coloration was due to absorption by
water vapor.

For a modern treatment of the subject, see the
Meinels' book.
They cite the full report compiled by the Royal Society, and discuss the
explanation that is accepted today for these curious and somewhat rare
displays.
As they point out, both bluish and greenish colors can appear.

Green aurorae

Aurorae are much fainter phenomena that are
visible only when the sky is completely dark, or nearly so.
Jan Curtis
has a fine auroral website, with a great collection of links as well as
photographs.
Once again, I refer you to the
Meinels' book, which has
photographs of most of the phenomena discussed here: green flashes,
crepuscular rays, and green aurorae.

Green artifacts

Finally, sometimes green errors occur in pictures that can fool
the unwary. These imaging
artifacts are particularly common in
digital images and videos.
You can't accept pictures at face value — particularly if they
show features that were not seen by the eye of the observer.